Process for reactivation of soda-lime

ABSTRACT

A MOISTURIZING MEDIUM, E.G. STEAM IS INJECTED INTO A SODA-LIME TREATMENT BED AFTER THE SODA-LIME THEREIN HAS BEEN USED TO REMOVE H2S AND/OR COS IMPURITIES FROM A NORMALLY GASEOUS HYDROCARBON FEED STREAM. THE SODA-   LIME IS THEREBY REACTIVATED RESULTING IN A LONGER CYCLE LIFE OF THE BED.

May 21, 1914 E. H. GRLEY ETAL 3,812,200

PROCESS FOR REACTIVATION 0F SODA-LIME Filed Aug. 23, 1972 [ll TRANCE 5715/4/14 EX/T United States Patent 3,812,200 PROCESS FOR REACTIVATION OF SODA-LIME Edward H. Grey, Media, and Robert C. Shufelt, Brookhaven, Pa., assignors to Sun Oil Company of Pennsylvania, Philadelphia, Pa.

Filed Aug. 23, 1972, Ser. No. 283,255 Int. Cl. C07c 11/00 US. Cl. 260-677 A 4 Claims ABSTRACT OF THE DISCLOSURE A moisturizing medium, e.g. steam is injected into a soda-lime treatment bed after the soda-lime therein has been used to remove H 8 and/or COS impurities from a normally gaseous hydrocarbon feed stream. The sodalime is thereby reactivated resulting in a longer cycle life of the bed.

BACKGROUND OF THE INVENTION The demand for propylene as feed stock for the growing polypropylene industry has increased steadily in recent years. An important source of this basic material is the C hydrocarbons produced in the various refining and cracking processes to which petroleum oils are subjected. These petroleum gases contain appreciable quantities of sulfur containing compounds which must be removed in order to produce an acceptable feedstock for further processing or to produce a commercially acceptable product.

In addition to the Well-known sulfur compounds such as hydrogen sulfide and mercaptan, there is a small quantity of carbonyl sulfide (COS). Usually COS is present in these hydrocarbon gases to the extent of only several hundred parts per million (p.p.m.) by weight but often this amount is beyond the allowable limits of an acceptable product for its intended use, e.g., as a monomer in polypropylene production. Since carbonyl sulfide is almost always formed when carbon, oxygen, and sulfur or their compounds such as carbon monoxide, carbon disulfide are brought together at high temperatures, this compound is most frequently found in the gases from thermal and/or catalytic cracking operations, although, in some cases, it has been noticed in virgin petroleum fractions.

To some extent, carbonyl sulfide is not as reactive as its companion in hydrocarbon gases, hydrogen sulfide. According to Kirk-Othmers Encyclopedia of Chemical Technology, Volume 13, pages 384 to 386, 1954 edition, carbonyl sulfide reacts slowly with aqueous alkali-metal hydroxides and is only slowly hydrolyzed to carbon dioxide and hydrogen sulfide. This relatively unreactive characteristic of carbonyl sulfide makes it extremely difficult to remove from petroleum streams by conventional desulfurization techniques.

It is known that carbonyl sulfide as well as hydrogen sulfide can be effectively removed from normally gaseous carbonyl sulfide-containing hydrocarbons by contacting them with soda-lime. One such proces is disclosed in U.S. 3,315,003 issued Apr. 18, 1967 to H. M. Khelghatian. In one application of that process, a mixture of normally gaseous hydrocarbons composed mainly of C C and a small amount of C hydrocarbons is charged in liquid phase to a separation zone in intimate contact with, say, aqueous monoethanolamine. The MBA is preferably a 20% solution and is usually recycled for more efiicient operation. This MBA-scrubbing removes from the mixture of hydrocarbons most of the acid gases H S, CO etc. and part (from 20% to 90%) of the carbonyl sulfide. These MBA-scrubbed hydrocarbons of reduced carbonyl sulfide content are then passed into a first distillation zone, i.e., a de-ethanizer, wherein the C and lighter components, i.e.,

those hydrocarbons containing primarily less than three.

carbon atoms per molecule plus residual acid gases are removed overhead and the C and heavier hydrocarbons are removed as a bottoms product composed mainly of propane and propylene. The bottoms product from the first distillation zone is then passed into a second distillation zone wherein a liquefied hydrocarbon stream comprising essentially propane is separately withdrawn as a bottoms product which is sent to, say, LPG (liquefied petroleum gas) storage. A hydrocarbon stream comprising essentially propylene, e.g. 99+% propylene, is separately withdrawn as an overhead product. The propylene is then passed in liquid phase into a contact zone containing sodalime to remove essentially all of the remaining carbonyl sulfide and hydrogen sulfide. The treated propylene is passed into a drying zone containing, say, molecular sieves, whereby moisture is essentially removed. The recovered propylene is now essentially free of H 8 and COS, and is essentially moisture-free.

The term soda-lime as used herein is defined as lime which has added thereto sodium hydroxide and sometimes is described as a mixture of soda and lime. The mixture should be in pellet form of from 5 to 20 mesh size, preferably 8-12 mesh. The term lime includes quick lime and hydrated lime. Lime is prepared from limestone which is a rock composed of at least 50% calcium carbonate with varying percentages. of impurities present. Limestone in its broadest sense includes any calcium containing material such as marble, chalk, travertine, coral, etc. These limes may contain from 5% to 45% magnesium carbonate. Usually, however, limestone refers to stratified calcareous rock composed mainly of the mineral calcite. Upon calcination, limestone yields the lime of commerce.

The calcination of limestone under carefully controlled conditions drives ofl carbon dioxide leaving primarily calcium oxide and magnesium oxide, otherwise known as quicklime. Treating quicklime with enough water to satisfy its chemical afiinity for water produces a dry powder known as hydrated lime. Hydrated lime is essentially calcium hydroxide or a mixture of calcium hydroxide, magnesium oxide, and magnesium. hydroxide.

The soda-lime of the present invention consists of lime obtained as above described which has added thereto a minor amount of sodium hydroxide. The amount of sodium hydroxide calculated as sodium may vary from 1% to 10% but is preferably from 2% to 4%. The soda-lime may contain minor amounts of potassium. A typical sample of soda-lime used herein for illustration purposes, contains from 2.5% to 3.2% sodium hydroxide calculated as sodium with the remainder being calcium hydroxide, a small amount of potassium hydroxide, and water, either as water of hydration and/ or free moisture. The water of hydration may amount to 14% to 18% with the free moisture content varying between 0.5% to 5%. The soda-lime used in this invention is a commercially available commodity.

SUMMARY OF THE INVENTION It has now been found that moisturizing of the sodalime bed during use in the aforementioned process substantially increases the on-stream life of said bed.

More particularly, it has been found that injection of steam, and preferably saturated steam, into a bed of soda-lime in situ, after said bed has dropped in efiiciency to the point of needing replacement, re-activates the bed, often allowing more than 50% additional on-stream time.

Therefore, it is an object of the present invention to provide a process for re-activation of a soda-lime bed used for removal of hydrogen sulfide and carbonyl sulfide from normally gaseous hydrocarbons, in liquefied or gaseous state, preferably in liquefied state.

It is a further object to provide a process for maintaining a higher level of efficiency in a given H 8 and COS removal bed through a program of intermittent moisturizing-reactivation treatments of said bed.

DESCRIPTION OF THE DRAWING In normal absorber operation, a propylene/propane stream enters the process via line 1 and is allowed to enter absorber 3 through valve 2 which is in the open position. Valve 10 is closed. The propylene/propane stream, containing H 8 and COS impurities then passes through the absorber which is filled with soda-lime. The effluent exits via line 4 through open valve 5 to further processing. Valve 6 is closed.

In the moisturizing-reactivation process of this invention, valves 2 and 5 are closed and a moisturizing stream such as steam passes through open valve 6 and via lines 7 and 4 into the absorber bed, 3. The moisturizing stream passes through said bed, exits via line 8 through line 9 and open valve 10 and is discharged. The moisturizing stream can also pass in an upward motion through the bed and neither the direction of flow nor the specific arrangement of valves shown in the drawing is meant to be limiting of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A propylene propane refinery stream containing less than about 20 p.p.m. of H S was treated in a soda-lime absorber containing approximately 10,000 pounds of sodalime. The treatment takes place in the liquid phase at a pressure in the range of about 250 to 300 p.s.i.g. and a temperature in the range of about 100 to 120 F.

Test runs of the invention were made on two commercial soda-lime treaters to illustrate the utility of the invention and the advantage gained by its implementation.

In Treater 1, 134,300 barrels of the previously described refinery stream were treated with satisfactory removal of H S before the bed lost its effectiveness and went sour. The moisturizing process was commenced on the bed in situ, and 40 p.s.i.g. saturated stream was injected for 10 to 13 hours at which time moisture was noted at the steam exit and the process was stopped. After reactivation through moisturizing, an additional 76,000 barrels of the propylene/propane stream were treated with satisfactory removal of H S in the reactivated bed. This represents an economic advantage as well as a time advantage since the number of bed charges is reduced significantly.

In Treater 2, a typical run lasted for 143,000 barrels of charge. Two separate reactivation steps were performed on this unit increasing the life of the bed from the normal 143,000 to 269,000 barrels. Each moisturizing step in both examples was carried with saturated steam at a bed temperature in the range of to F. for a period of about 10 to 13 hours, the time needed for moisture to work through to the bottom of the bed.

A person skilled in the art can adapt his conditions to fit a given soda-lime bed through minimal experimentation. Suitable conditions for the hydrocarbon treatment are known in the art. Suitable conditions for the moisturizing conditions which will tend to maintain the desired temperature of the soda-lime bed for hydrocarbon treatment are employed.

As is well shown by these two examples, moisturizingreactivation of soda-lime treater beds results in significant increases in the lives of those beds and represents a substantial advance in the state of the art.

We claim as our invention:

1. A process for the reactivation of a soda-lime bed, which has been used to remove H S or COS or both from normally gaseous hydrocarbons, wherein said bed is exposed to steam, thereby being activated in situ, resulting in increased cycle life.

2. The process of claim 1 wherein said bed is exposed to saturate steam.

3. The process of claim 1 wherein said steam is contacted with said soda-lime bed at regular intervals during the treatment cycle thereby increasing the length of said cycle.

4. The process of claim 3 wherein said steam is saturated steam.

References Cited UNITED STATES PATENTS 3,315,003 4/1967 Khelghatian 260-677 A 3,725,529 4/1973 Giammarco et a1. 423-223 507,331 9/1893 Salomon 423-220 3,000,988 9/1961 Garchmer et al. 260-677 A 2,301,588 11/1942 Schulze et a1 208-236 2,884,377 4/1959 Bozich et a1. 208-230 3,185,641 5/1965 Cowden 208-230 3,658,694 4/1972 McCrear et al. 208-230 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner US. Cl. X.R. 

